Cardiovascular disease claims the lives of nearly 500,000 women each year, yet it is still often considered a male health concern. Much of this apparent "gender bias" stems from the fact that only 10% of women experience significant cardiovascular morbidity or mortality before menopause, compared to 33% for men of comparable age. Within a few years after reaching menopause, however, the incidence of hypertension and coronary heart disease in women rises precipitously, and by the age of 65 a woman becomes just as vulnerable to cardiovascular mortality as a man. Interestingly, no pathophysiological findings can account for this lost protection. Thus, it has been proposed that estrogens somehow delay and/or protect against the progressive deterioration of cardiovascular function so often associated with aging. Recent evidence suggests that much of the total cardiovascular benefit of estrogen therapy is related to hemodynamic effects, yet we know very little about estrogen-induced vasodilation. For example, estrogen increases cardiac blood flow by relaxing coronary artery smooth muscle (CSM) through an undefined mechanism. In contrast, our preliminary findings now provide the first evidence for a molecular mechanism that could mediate estrogen-induced relaxation of CSM: stimulation of BK(Ca) potassium channel gating through cyclic GMP-dependent phosphorylation. The proposed experiments will identify and characterize molecular mechanisms of estrogen-induced CSM relaxation at the tissue, cellular, and molecular level. The ionic basis for relaxation will be characterized in intact coronary artery preparations, and these findings will then be reexamined at the cellular level by measuring whole-cell potassium currents directly with the perforated patch configuration of the patch-clamp technique. Furthermore, the specific ion channel(s) modulated by estrogen will be identified via single- channel measurements, and signal transduction mechanisms will be characterized in intact arteries, single CSM cells, and cell-free membrane patches. Preliminary results suggest that estrogen stimulates nitric oxide production, which stimulates synthesis of cyclic GMP and cyclic GMP-dependent protein kinase activity. Phosphorylation of BK(Ca) channels enhances their activity and leads to vasodilation. The long- term goal of this study is to better understand how estrogen prevents and/or delays age-related cardiovascular dysfunction. It is hoped that these studies will provide the impetus to develop new therapeutic regimens for the treatment of coronary heart disease and other pathophysiological conditions associated with estrogen deficiency, e. g., osteoporosis, menopausal complications, menstrual problems.